Coronal Multiplane Reconstructed CT Image Determining Lateral Vertebral Notch-referred Pedicle Screw Entry Point In Subaxial Cervical Spine:A Preclinical Study

Study Design: This is a prospective study which combined radiographic imaging?cadaver-based morphology and clinical medicine.Backgrounds: The first report of pedicle screw insertion through the C3 to C6 was the description of techniques and report of 13 cases of pedicle fixation for traumatic lesions of the lower cervical spine by Abumi et al.[1] in 1994.And after that,the use of pedicle screws in the cervical spine is increasing accepted among spine surgeons.However,compared to the lumbar and thoracic spine,the use of pedicle screws in the cervical spine still has been considered too risky due to the surrounding neurovascular structures.Severe complications in the subaxial cervical spine with the use of cervical pedicle screw would be caused,if those important structures be injured.Furthermore,radiographic image or cadaver-based morphometric measurements used to guide the surgeon in pedicle screw(PS)insertions show significant variability.The most consistent anatomic landmark and the most practical and easy-mastering technique of cervical PS placement still need identify.Objectives: To measure new parameters of subaxial cervical PS entrance localization and trajactory parameters,and evaluate the feasibility of vertebral lateral notch-referred technique for PS insertion.Methods: Forty cervical CT scans from volunteers were performed in axial,sagittal and coronal plane.Entrance localization of subaxial cervical spine was determined through quantitating the PS insertion point related with the lowest point of vertebral lateral notch(VLN)in the coronal multiplane reconstruction images(CMRI).Axial and sagittal parameters were measured to illuminate the trajactory of PS insertion,coronal plane scans can be used to measure other parameteres.All parameters include distance X(horizontal distance from the PS insertion point to the lowest point of VLN in the coronal plane),distance Y(vertical distance from the pedicle projection center(PPC)to the lowest point of VLN),outer pedicle width(OPW),outer pedicle height(OPH),inner pedicle width(IPW),inner pedicle height(IPH),pedicle mediolateral angle(?),pedicle cephalocaudad angle(?).On the basis of above analysis,twelve human cadaveric subaxial cervical specimens were inserted with PS by using the vertebral lateral notch-referred technique.Thereafter,cortical integrity of each pedicle was evaluated by anatomic dissection of the specimens.The cortical penetration was classified into four grades.Grade 0: cortex is of integrity;Grade I: screw threads or less than one-fourth of the screw cross section penetrates the cortex;Grade II: more than one-fourth but less than one-second of the screw cross section penetrates the cortex;Grade III: more than one-second of the screw cross section penetrates the cortex.Results: The mean values of OPW,OPH,IPW and IPH are gradually increased from C3 toward C7.The mean ? angle is largest at C4,then at C3 and are gradually decreased from C5 to C7.The mean ? angle is gradually caudal to cephalad from C3 to C7.The distance X is almost consistent with value around 2.2 mm medial to the lowest point of notch from C3 to C7.The distance Y is around 1.4 mm lower to the lowest point of notch from C3 to C6,but around 0.12 mm higher at C7.A total of 120 pedicle screws were inserted.The cortical penetration rate is 78.33% in grade 0,10.0% in grade I,8.33% in grade II and the poor position of pedicle screw is only 3.33% in grade III.Conclusion: CMRI can be used as a reliable preoperative reference for guiding PS insertion.The notch may be a consistent landmark for the notch-referred technique which is practical and easy-mastering for subaxial cervical spine PS placement.